1. Field of the Invention
This invention relates to a digital displacement sensor for converting the displacement of a moving member into a digital signal commensurate with the displacement of the moving member and, more particularly, to a device for converting the opening angle of a throttle valve of a motor vehicle or other transporting vehicle into a digital signal.
2. Description of the Prior Art
A typical digital displacement sensor which has been employed widely hitherto is a displacement detector having digital electrical contacts and consisting of a plurality of stationary electrodes electrically insulated from each other, and a moving element having a brush and adapted to slide on the electrodes. However, such a displacement detector suffers from disadvantages such as excessive wear of the contacts and noise developed upon the opening and closing of the contacts. On the other hand, for avoiding the aforesaid disadvantages, there have been proposed various types of non-contact type displacement sensors. Inductosyn (Trade Mark) is one of the examples, in which a stationary element having a zigzag coil formed in a plane and a moving element are arranged in opposing but spaced relation to the coil surface, so that the displacement of the moving element is detected by utilizing the variation in mutual inductance depending on the relative positions of the zigzag coil.
However, such a sensor provides only an output signal having the alternatives of a 0 or a 1 depending on the displacement of the moving element, so that it is imperative to provide a sensor for sensing the moving direction of the moving element and a device for calculating and storing an output signal, for the purpose of detecting the direction and extent of displacement of the moving element, resulting in a complicated construction.
In addition, there has been proposed an encoder type sensor utilizing light beams. This, however, poses other disadvantages such as premature deterioration of a light source, and the need to use extremely high precision for relative alignment of the position of a light source with that of an encoding plate. This poses still another problem in materializing a photo-detector which has a rapid response and withstands a high ambient temperature. Accordingly, those attempts are not suitable for detecting the opening angle of a throttle valve rapidly.